The proposed study is a continuation of a project funded by the National Institute of Child Health and Development. This current study has investigated the relationship among sleep state organization and physiological stability, and environmental perturbations among preterm infants in the Neonatal Intensive Care Unit (NICU). The first goal was to comprehensively investigate sleep state organization of the infants from about 29 weeks CA to 35 weeks CA. Infants were monitored for 48 continuous hours in the NICU for respiration, heart beats (from electrophysiological recordings), body movement (from sensor mattress and from time lapse video recording), and eye movements (video recording). All caretaking activities were also monitored on videotape. A strategy for classifying sleep/wake states was used which proved to be very sensitive in detecting state organization in preterm infants. Using the infant's own data for comparison, regularity/variability of certain state variables was determined by statistical properties of those state variables. Specifically, parameters from the distribution of 1-minute scores gathered over 24 hours of respiration rate variability (RRV) and heart rate variability (HRV) were used to define the regularity of respiration and heart rate. States were assigned to each minute over a 24-hour period. To further investigate state organization, microanalytic analysis of state organization focussed on (1) the investigation of the statistical properties of individual state variables; (2) the clustering of sleep state variables (the co- occurrence of patterns for a specific state for each state variable) of RRV, HRV, body movement and eye movement; and (3) the relationship of instantaneous heart rate and respiration rate (sinus arrhythmia) and between heart rate and amound of body movement. Novel statistical approaches have been proposed to further elucidate these phenomena. A continuation of this project is proposed to (1) further develop statistical approaches to elucidate the phenomena of clustering of state variables, periodic structure of state variables, sinus arrhythmia, body movement-heart rate synergy, (2) increase the subject pool to include younger infants (less than 32 weeks conceptual age), (3) develop a more refined quantitative measure of body movement, (4) extend the population of subjects to include infants of drug abuse mothers, a population known to have sleep disorders, and (5) assess sleep state organization and the incidence of physiologic disturbance as a function of amount of ambient stimulation in the NICU.